To estimate the risk of consuming a disease-inducing-serving of beef
during the British Mad Cow Epidemic, we will use
the ratio
of the number of disease-inducing-servings
of beef consumed during the epidemic to the total number of beef servings
produced by
Britain during the epidemic. In order to accomplish this, we must make
several assumptions.

The most important assumption concerns our ratio's denominator.
We need that the consumption of beef occurs in quantifiable
servings, and, more importantly, we need that each of these servings is
EQUALLY LIKELY
to be consumed by a given consumer. Clearly this is a serious
assumption.
Some consumers eat only
steaks cut from organically grown cattle, while others eat only sausage
from fast food restaurants.
Our estimate seems likely
to be overestimating your risk if you consume only organic steaks and
underestimating your risk if you consume only
sausage from fast food restaurants. We are forced to view our number as the risk
associated to some sort of "average consumer".

To estimate the numerator means we need to quantify how many servings were
disease-inducing-servings of beef. This requires us to assume that
cases of CJD associted to the epidemic were caught from a particular
serving. It may be that several
exposures are in fact necessary before catching the disease.
Or it may be that
the dissease is the result of some inherent inabiltiy of
certain individuals' bodies to cope with this prion's presense, which was
not really the "serving's fault". However, barring any additional medical
data, this assumption seems
reasonable.